The present invention is related to automatic gear checking machines and in particular to a machine attachment for automatically checking the true index tooth spacing of both internal and external gears, and other similar components. A true index reading is obtained because the finger of a sensing probe is utilized to engage each tooth of the gear along a constant radius index line. The amount of pressure that is applied to the finger by the gear is translated into a voltage signal by a differential sensing transformer.
In a true index gear tooth space checking machine it is very desirable to be able to check a large range of gear sizes with the same checking machine. It is also advantageous to make such checks while the gear is constantly moving in order to minimize the checking time. Other desirable features in such a checking machine include the ability to check special gear segments with any number of teeth and the ability of obtaining a highly accurate true index reading without first going through one full revolution in order to set the index points. The machine of the present invention is able to utilize all of the above-noted advantages; and in addition, the machine is relatively simple in construction and does not require optical devices or complex mechanical configurations or linkages.
This invention involves a gear checking machine which is particularly useful in measuring helical lead and involute gears, especially large gears, those on the order of 40 to 60 inches or more in diameter. The measurement of the helical lead and of the involute both require an accurate timed relationship between a rotating axis and linearly driven test probe. Prior art involute checkers utilize a ratio bar in conjunction with a master base circle sector or disc. This type of machine had physical limitations which placed severe limitations on the accuracy of the machine and the configuration of the gear support table in the measurement of large gears on the order of 40 to 60 inches or more in diameter. The timed relationship between a rotating axis and linear motion of the helical lead testing machines of the prior art is generally accomplished by a sine bar unit which transmits an accurate angular measurement. Machines incorporating these devices are to be seen in U.S. Pat. Nos. 2,787,060 and 2,998,657.
The present invention eliminates the ratio bar and sine bar and utilizes a large disc or base circle which is coupled to the gear support table. The large base circle is operatively attached to an encoder which accurately registers by electronic pulses the angular or rotary movement of the base disc. The input of this encoder advantageously is achieved by utilizing a very small diameter disc which is normally driven by the outer periphery of the large base disc. This large ratio between the base disc and the encoder disc provides a large range of accuracy in determining the angular movement of the disc.
Two simple discs with properly calculated diameters rotating with each other can provide a much wider range of ratio and accuracy than that obtainable by another device.
A number of advantages are gained by this device in proportioning, manufacturing and in assembly. These are:
1. Flexibility - large ratio range can be obtained. PA1 2. Exact sizes of table and encoder discs are not required because encoder pulses for one revolution of table are counted by a circuit in an electrical panel and inserted into ratio formula. PA1 3. Round configuration - easy to make - easy to manufacture. PA1 4. Positive drive can be obtained by holding the discs in contact by means of springs, adjustable pressure bar, weights, etc.
Thus, it is seen that incorporation of base disc principle in conjunction with stepping motors and gear boxes, provides a wide range of proportioning at a very low cost not possible with other known methods. ss
In the machine of the present invention an encoder is attached to a rotary support table which supports the gear that is being checked. The table is driven by a variable speed motor and the encoder produces a predetermined number of pulses per revolution of the table. The total number of pulses that is supplied by the encoder is divided by the number of teeth in the gear being checked so as to provide a specified number of pulses per each gear tooth.
To set up the machine for gear tooth space checking a space checking probe is positioned in the gear tooth space of a first tooth at an appropriate depth so that the end of the finger is placed along a predetermined index line. The machine is then started and the table is rotated so that te probe comes into contact with the gear tooth. At the time the probe comes into contact with the gear tooth, a recording pen is moved to the center of a strip of recording paper, and the probe is withdrawn from the gear under the control of a counter which counts the number of encoder pulses that are generated. The rotary support table starts to turn, and after a predetermined number of pulses per tooth are counted the indicating finger will proceed into the next tooth space so that the end of the sensing finger is again along the true index line. The probe is again moved forward to its forward stop location where the sensing finger waits until it contacts the next gear tooth as the table continuously rotates.
When the probe contacts the next gear tooth, the motion of the probe displaces a magnet in a linear variable differential transformer that is housed in the probe. The resulting output signal from the differential transformer is sent to a recorder so that the pen produces an appropriate recording mark on the recording paper which indicates the displacement of the end of the sensing finger from the nominal true index point. After the counter has reached a count that indicates that the gear has been completely revolved around 360.degree. the machine is shut off, the probe is retracted and the counter is reset. The probe is driven forward and is withdrawn by a constantly rotating motor which drives an eccentric that is coupled to the probe. The motion of the slide mechanism that carries the probe forward and backward actuates limit switches which initiate operations that actuate and deactuate a clutch and a brake coupled to the output shaft of the motor at the proper time.